ABSTRACT: Introduction:This paper examines one of the NHS England Pioneers programmes of Integrated Care, which was implemented in three localities in East London, covering the area served by one of the largest hospital groups in the UK and bringing together commissioners, providers and local authorities. The partners agreed to build a model of integrated care that focused on the whole person. This qualitative and participatory evaluation looked at how an ambitious vision translated into the delivery of integrated care on the ground. The study explored the micro-mechanisms of integrated care relationships based on the experience of health and social care professionals working in acute and community care settings. Methods:We employed a participatory approach, the Researcher in Residence model, whereby the researcher was embedded in the organisations she evaluated and worked alongside managers and clinicians to build collaboration across the full range of stakeholders, develop shared learning, and find common ground through competing interests, while trying to address power imbalances. A number of complementary qualitative methods of data generation were used, including documentary analysis, participant observations, semi-structured interviews, and coproduction workshops with frontline health and social care professionals to interpret the data and develop recommendations. Results:Our fieldwork exposed persistent organisational fragmentation, despite the dominant rhetoric of integration and efforts to build a shared vision at senior governance levels. The evaluation identified several important themes, including: a growing barrier between acute and community services; a persisting difficulty experienced by health and social care staff in working together because of professional and cultural differences, as well as conflicting organisational priorities and guidelines; and a lack of capacity and support to deliver a genuine multidisciplinary approach in practice, despite the ethos of multiagency being embraced widely. Discussion:By focusing on professionals' working routines, we detailed how and why action taken by organisational leaders failed to have tangible impact. The inability to align organisational priorities and guidelines on the ground, as well as a failure to acknowledge the impact of structural incentives for organisations to compete at the expense of cooperation, in a context of limited financial and human resources, acted as barriers to more coordinated working. Within an environment of continuous reconfigurations, staff were often confused about the functions of new services and did not feel they had influence on change processes. Investing in a genuine bottom-up approach could ensure that the range of activities needed to generate system-wide cultural transformation reflect the capacity of the organisations and systems and address genuine local needs. Limitations:The authors acknowledge several limitations of this study, including the focus on one geographical area, East London, and the timing of the evaluation, with several new interventions and programmes introduced more or less simultaneously. Some of the intermediate care services under evaluation were still at pilot stage and some teams were undergoing new reconfigurations, reflecting the fast-pace of change of the past decade. This created confusion at times, for instance when discussing specific roles and activities with participants. We tried to address some of these challenges by organising several workshops with different teams to co-interpret and discuss the findings.